Among conventional engines equipped with a supercharger, such as a turbocharger, have been those provided with an exhaust bypass passage for bypassing a turbine of the supercharger. In the exhaust bypass passage, a waste gate valve for opening and closing the exhaust bypass passage is provided. Upon opening/closing of the waste gate valve, an excessive rise in the boost pressure is suppressed to ensure stability of the boost pressure and inhibit damage to the engine or the supercharger itself.
In recent years, it has been common practice to actively control the opening/closing action of the waste gate valve in accordance with the operating state of the engine. There has been, for example, a controller of the type which detects an ambient temperature and controls the opening of the waste gate valve in accordance with the detected ambient temperature, thereby preventing the occurrence of malfunction due to a change in the temperature of an intake system (see Patent Document 1).